Cooking on grills such as barbecue grills generally is done by impringing a flame against ceramic briquettes or various types of metal surfaces, typically using propane, natural gas or charcoal as an energy source or fuel for combustion. When food is cooked on a grill, it is desirable first to sear the outside of the food to lock in the juices and further to cook the food as evenly as possible to avoid having the outer portions of the food burned while the inner portions are left uncooked. In most conventional grills, the food is cooked primarily using hot gases created by the flames and products of combustion from the burning of the fuel heating the ambient air within the grill.
Unlike cooking with heated gases, as done with most conventional grills, cooking with infrared radiation enables more even heating over the surface of the food so the food can be cooked evenly, with the outside first being seared. In most conventional grills, however, there typically is very little infrared radiation generated. Conventional grills include ceramic briquettes or "lava rocks" designed to be heated by burning the gas/fuel to radiate heat. Such ceramic briquettes, however, tend to generate little infrared energy and possess poor thermal conductivity, which limits the conduction of heat throughout the briquettes. Also these briquettes possess poor thermal inertia. As a result of the poor thermal inertia of the briquettes, as liquids impinge and evaporate on the surface of the briquettes, the briquettes are cooled below the ignition temperature of the oils that drip from the food onto the briquettes. As oils and/or liquids drip from the food, they tend to be absorbed into the ceramic briquettes and build up on the briquettes, which buildup can ignite and cause flame flare ups. Accordingly, such ceramic briquettes generally have to be changed at periodic intervals. Some conventional grills utilize metal plates that are impinged and heated by the flames and products of combustion. Such metal plates, however, also are poor emitters of infrared radiation, and generally are used, as with the ceramic briquettes, for the purpose of evaporating juices and incinerating fats that fall upon them from the cooking meats to create vapors that are then directed over the surfaces of the food to impart an "outdoor" or smoked flavor.
Gas grills have been developed which utilize under-fired burner assemblies designed specifically to generate infrared radiant energy for cooking food. For example, U.S. Pat. Nos. 4,321,857 and 4,886,044 to Best disclose infrared gas grills which cook food using infrared radiant energy. In addition, electric cooking units, including overhead type broilers and ovens, also use infrared radiant energy for cooking foods. In cooking with infrared radiant energy, infrared radiant energy having longer wavelengths is readily absorbed within the surface of the food to generate heat that is conducted inwardly, resulting in the surface of the meat being rapidly seared to seal in the juices while the meat is cooked from the outside toward the center. One problem with conventional under-fired infrared grills and other cooking devices generally is that these devices can have a low level of thermal inertia or have a heating element that is positioned out of contact with the juices and fats that drip from the meat or other food being cooked, such that the juices and fats are not vaporized or burned to create vapors that pass over the food to impart flavor.
In addition, in gas grills using an infrared radiant heating or burner element, the burner element usually is formed from a ceramic material. Similarly in the case of overhead broilers, a glass or ceramic type coating has been used to cover the emitting surface in some applications. For example, Japanese Patent No. JP 57000430A discloses an overhead burner with a glass or ceramic type coating. Conventional under-fired burners are, however, subject to failure if they become wet as water is absorbed into the ceramic elements, which causes the elements to swell, ultimately leading to failure of the ceramic element. Another problem with an infrared radiant grill is employing a ceramic emitter that can be susceptible to the effects of wind and rain, which can cause the combustion of gas by the burner elements to be diminished, affecting the cooking of the food by the grill. A further limitation of such burner elements is that the turn-down ratio from high fire to low fire is generally limited, since most radiant ceramic burners usually will not operate efficiently below a surface temperature of about 1100.degree. F. without becoming unstable. In the cooking of meats such as steak, a high fire generally is desired. When it is necessary to cook more slowly over lower heats, however, such lower heats are often difficult to achieve and maintain because of the limited turn-down ability of such burners. According, it can be seen that a need exists for an improved cooking apparatus that overcomes these and other problems in the art.